Move common functionalities to base APIModel
Move common functionalities to base APIModel

This commit adds new file base.py which holds the common
functionalities w.r.t API models.
1. Checking for distributed Architecture here instead of all api_models
2. Move rpc calling to base, which can be used by all api models.

All api models can be made to inherit from this base api class to
reuse the functionality and with minimal changes to all other api models.

Change-Id: I4d6336a4048845143e3ade2454a0f7f2d82aba52

ramineni/my_congress,ramineni/my_congress,ramineni/my_congress,ramineni/my_congress,openstack/congress,openstack/congress